Patch "ftrace: Fix possible use-after-free issue in ftrace_location()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    ftrace: Fix possible use-after-free issue in ftrace_location()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ftrace-fix-possible-use-after-free-issue-in-ftrace_location.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From e60b613df8b6253def41215402f72986fee3fc8d Mon Sep 17 00:00:00 2001
From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Date: Fri, 10 May 2024 03:28:59 +0800
Subject: ftrace: Fix possible use-after-free issue in ftrace_location()

From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>

commit e60b613df8b6253def41215402f72986fee3fc8d upstream.

KASAN reports a bug:

  BUG: KASAN: use-after-free in ftrace_location+0x90/0x120
  Read of size 8 at addr ffff888141d40010 by task insmod/424
  CPU: 8 PID: 424 Comm: insmod Tainted: G        W          6.9.0-rc2+
  [...]
  Call Trace:
   <TASK>
   dump_stack_lvl+0x68/0xa0
   print_report+0xcf/0x610
   kasan_report+0xb5/0xe0
   ftrace_location+0x90/0x120
   register_kprobe+0x14b/0xa40
   kprobe_init+0x2d/0xff0 [kprobe_example]
   do_one_initcall+0x8f/0x2d0
   do_init_module+0x13a/0x3c0
   load_module+0x3082/0x33d0
   init_module_from_file+0xd2/0x130
   __x64_sys_finit_module+0x306/0x440
   do_syscall_64+0x68/0x140
   entry_SYSCALL_64_after_hwframe+0x71/0x79

The root cause is that, in lookup_rec(), ftrace record of some address
is being searched in ftrace pages of some module, but those ftrace pages
at the same time is being freed in ftrace_release_mod() as the
corresponding module is being deleted:

           CPU1                       |      CPU2
  register_kprobes() {                | delete_module() {
    check_kprobe_address_safe() {     |
      arch_check_ftrace_location() {  |
        ftrace_location() {           |
          lookup_rec() // USE!        |   ftrace_release_mod() // Free!

To fix this issue:
  1. Hold rcu lock as accessing ftrace pages in ftrace_location_range();
  2. Use ftrace_location_range() instead of lookup_rec() in
     ftrace_location();
  3. Call synchronize_rcu() before freeing any ftrace pages both in
     ftrace_process_locs()/ftrace_release_mod()/ftrace_free_mem().

Link: https://lore.kernel.org/linux-trace-kernel/20240509192859.1273558-1-zhengyejian1@xxxxxxxxxx

Cc: stable@xxxxxxxxxxxxxxx
Cc: <mhiramat@xxxxxxxxxx>
Cc: <mark.rutland@xxxxxxx>
Cc: <mathieu.desnoyers@xxxxxxxxxxxx>
Fixes: ae6aa16fdc16 ("kprobes: introduce ftrace based optimization")
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/trace/ftrace.c |   39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1565,12 +1565,15 @@ static struct dyn_ftrace *lookup_rec(uns
 unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 {
 	struct dyn_ftrace *rec;
+	unsigned long ip = 0;
 
+	rcu_read_lock();
 	rec = lookup_rec(start, end);
 	if (rec)
-		return rec->ip;
+		ip = rec->ip;
+	rcu_read_unlock();
 
-	return 0;
+	return ip;
 }
 
 /**
@@ -1583,25 +1586,22 @@ unsigned long ftrace_location_range(unsi
  */
 unsigned long ftrace_location(unsigned long ip)
 {
-	struct dyn_ftrace *rec;
+	unsigned long loc;
 	unsigned long offset;
 	unsigned long size;
 
-	rec = lookup_rec(ip, ip);
-	if (!rec) {
+	loc = ftrace_location_range(ip, ip);
+	if (!loc) {
 		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
 			goto out;
 
 		/* map sym+0 to __fentry__ */
 		if (!offset)
-			rec = lookup_rec(ip, ip + size - 1);
+			loc = ftrace_location_range(ip, ip + size - 1);
 	}
 
-	if (rec)
-		return rec->ip;
-
 out:
-	return 0;
+	return loc;
 }
 
 /**
@@ -6784,6 +6784,8 @@ static int ftrace_process_locs(struct mo
 	/* We should have used all pages unless we skipped some */
 	if (pg_unuse) {
 		WARN_ON(!skipped);
+		/* Need to synchronize with ftrace_location_range() */
+		synchronize_rcu();
 		ftrace_free_pages(pg_unuse);
 	}
 	return ret;
@@ -6998,6 +7000,9 @@ void ftrace_release_mod(struct module *m
  out_unlock:
 	mutex_unlock(&ftrace_lock);
 
+	/* Need to synchronize with ftrace_location_range() */
+	if (tmp_page)
+		synchronize_rcu();
 	for (pg = tmp_page; pg; pg = tmp_page) {
 
 		/* Needs to be called outside of ftrace_lock */
@@ -7332,6 +7337,7 @@ void ftrace_free_mem(struct module *mod,
 	unsigned long start = (unsigned long)(start_ptr);
 	unsigned long end = (unsigned long)(end_ptr);
 	struct ftrace_page **last_pg = &ftrace_pages_start;
+	struct ftrace_page *tmp_page = NULL;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
 	struct dyn_ftrace key;
@@ -7375,12 +7381,8 @@ void ftrace_free_mem(struct module *mod,
 		ftrace_update_tot_cnt--;
 		if (!pg->index) {
 			*last_pg = pg->next;
-			if (pg->records) {
-				free_pages((unsigned long)pg->records, pg->order);
-				ftrace_number_of_pages -= 1 << pg->order;
-			}
-			ftrace_number_of_groups--;
-			kfree(pg);
+			pg->next = tmp_page;
+			tmp_page = pg;
 			pg = container_of(last_pg, struct ftrace_page, next);
 			if (!(*last_pg))
 				ftrace_pages = pg;
@@ -7397,6 +7399,11 @@ void ftrace_free_mem(struct module *mod,
 		clear_func_from_hashes(func);
 		kfree(func);
 	}
+	/* Need to synchronize with ftrace_location_range() */
+	if (tmp_page) {
+		synchronize_rcu();
+		ftrace_free_pages(tmp_page);
+	}
 }
 
 void __init ftrace_free_init_mem(void)


Patches currently in stable-queue which might be from zhengyejian1@xxxxxxxxxx are

queue-6.1/ftrace-fix-possible-use-after-free-issue-in-ftrace_location.patch




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